This invention relates, in general, to electronic device packaging, and more specifically to a structure and method for forming reliable interconnects in flip-chip type electronic packages.
Semiconductor chips usually are encapsulated in a device package prior to installation into an electronic system. Device or chip packages perform several key functions including, a) interconnective leads that allow the chip to be connected to the electronic system; b) physical protection; c) environmental protection; and d) heat dissipation. These functions present chipmakers with a number of design and manufacturing challenges that must be balanced with other factors such as cost.
Flip-chip packaging is one type of electronic chip packaging technology, and has been in existence for more than 30 years. Flip-chip packaging has progressed to include a wide variety of materials and methods for bumping, attaching and underfilling devices. Although the technology has progressed, challenges still exist in solving problems with higher frequency applications, tighter space requirements, reduced costs, and general device performance.
Current flip-chip package designs for semiconductor components include direct chip attach (DCA) structures. DCA refers to the direct attachment of an electronic chip to a circuit such as a printed circuit board (PCB) or a flex circuit. In typical DCA structures, metal studs such as gold studs are attached to the chip, and the structure is then encapsulated with a passivation material or mold compound. Next, openings are formed in the mold compound to expose the metal studs, and solder balls or bumps are then attached through the openings to provide contacts to the encapsulated chip. The solder bumps on the DCA device are then attached to the printed circuit board, flex circuit, or next level of assembly.
One problem with current DCA structures occurs at the solder ball/metal stud interface. For example, when the solder ball comprises a lead/tin alloy and the metal stud comprises gold, the gold tends to dissolve into the solder ball over time. This creates a gap between the gold stud and the solder ball, which leads to poor contact and weak joints. The poor contact and weak joints results in device reliability and performance problems.
Accordingly, a need exists for more reliable DCA structures. Additionally, a need exists for a cost effective and reproducible method of forming a more reliable DCA structure.